WASHINGTON -- U.S. officials received five severed fingers from four contractors abducted in Iraq more than a year ago, officials said.

The fingers were delivered last month to U.S. authorities in Iraq but weren't accompanied by a ransom note or other information, sources told The Washington Post. The fingers were partially decomposed when the U.S. officials received them.

The FBI is investigating and the families of the five U.S. contractors were notified, McClatchy news service reported.

Fingerprint and DNA analysis determined the fingers were removed from four of the five guards -- four Americans and one Austrian -- kidnapped Nov. 16, 2006, during an ambush near the Kuwaiti border. The fifth finger was from a U.S. contractor grabbed separately and reportedly held with the other missing men, sources said.

It hasn't been determined whether the fingers were removed while the men were alive or from their corpses.

"There's no way to accurately depict at this point whether it was prior to or after; scientifically I don't think they've been able to determine that," a source familiar with the investigation told the Post.